function dl=dnda(alpha,beta)
a=[.001 -.027 -.017 -.013 -.012 -.016 .001 .017 .011 .017 .008 .016
.002 -.014 -.016 -.016 -.014 -.019 -.021 .002 .012 .016 .015 .011
-.006 -.008 -.006 -.006 -.005 -.008 -.005 .007 .004 .007 .006 .006
-.011 -.011 -.010 -.009 -.008 -.006 .000 .004 .007 .010 .004 .010
-.015 -.015 -.014 -.012 -.011 -.008 -.002 .002 .006 .012 .011 .011
-.024 -.010 -.004 -.002 -.001 .003 .014 .006 -.001 .004 .004 .006
-.022 .002 -.003 -.005 -.003 -.001 -.009 -.009 -.001 .003 -.002 .001]';
s=.2*alpha;
k=fix(s);
if(k<=-2),k=-1;end
if(k>=9),k=8;end
da=s-k;
l=k+fix(1.1*sign(da));
s=.1*beta;
m=fix(s);
if(m<=-3),m=-2;end
if(m>=3),m=2;end
db=s-m;
n=m+fix(1.1*sign(db));
l=l+3;
k=k+3;
m=m+4;
n=n+4;
t=a(k,m);
u=a(k,n);
v=t+abs(da)*(a(l,m)-t);
w=u+abs(da)*(a(l,n)-u);
dl=v+(w-v)*abs(db);
